1. Field of the Invention
The present invention relates to a device for detection with time delay and phase integration.
2. Description of the Prior Art
In the prior art, known devices of this type usually comprise a plurality of linear arrays of detectors or detector strips which are parallel to each other, relative motion being intended to take place between the detectors and the image to be scanned. In other words, any one point of the image to be scanned is received sequentially by the detectors of any one row and the items of information or data collected at the different detectors are summated in synchronism with the movement of relative displacement.
This type of device is already known and is based on a principle designated in the literature as "Time Delay Integration" or TDI. The device makes it possible to multiply the integration time by a factor N which is equal to the number of detectors of each linear array or so-called row. Since reading noises are added quadratically, a gain in signal-to-noise ratio equal to .sqroot.N is obtained.
In the prior art, a charge-coupled shift register is usually placed between each row of detectors and the next row. The lateral inputs of this shift register are intended to receive the signals delivered by the detectors of any one row and these signals are added in synchronism by said register.
A problem is created, however, by the excessive bulk of registers having lateral inputs and placed between the rows of detectors.
This problem is particularly critical when the detection device is employed in the infrared region of the spectrum. In this region, the flux of photons received by the device is considerable and the same applies to the number of electric charges to be transported within each shift register. It is therefore found necessary to increase the width of the registers in order to permit storage of all the charges.
The present invention offers a solution to this problem.
In accordance with the invention, registers having lateral inputs and placed between the rows of detectors are no longer employed. For each row of detectors, provision is made for a charge-coupled device connected to the detectors by means of a single lead (or if necessary by means of two leads). This device is thus placed outside the photosensitive zone at a location other than between the rows of detectors. This arrangement accordingly has the effect of increasing the space available in the photosensitive zone and makes it possible, for example, to increase the charge integration time or to increase the resolution and therefore to improve the performances of the device.
It should also be pointed out that, in the prior art, the pitch adopted for the stages of the lateral-input shift registers placed between the rows of detectors was the same as the pitch or spacing between detectors. In accordance with the invention, the charge-coupled devices are no longer placed between the rows of detectors, with the result that the pitch of the register stages can be established without taking into account the pitch between detectors. In certain cases, it may be found necessary to employ a pitch of 25 micrometers between register stages whereas the pitch between the detectors is 100 micrometers. The result thereby achieved is to reduce the length of the charge-coupled devices and therefore their overall size. Efficiency of transfer is accordingly enhanced.